Unusually good trio in Tom’s lounge (7,4)
I believe the answer is:
sitting room
'lounge' is the definition.
(I know that lounge can be written as sitting room)
'unusually good trio in tom's' is the wordplay.
'unusually' indicates an anagram.
'good' becomes 'g' (abbreviation).
'g'+'trio'+'in'+'toms'='gtriointoms'
'gtriointoms' with letters rearranged gives 'SITTING-ROOM'.
(Other definitions for sitting room that I've seen before include "Lounge" , "Space with chairs, sofa" , "Parlour" , "Part of house" .)